It sounds to me like she is Dehydrated. Chest pain, headache and fatigue are all signs of dehydration, which can lead to a myriad of other problems. I agree with the others that she should see a medical professional. Though if you cannot see one soon, if she doesn't want to go to the ER or none of you trust the medical system (I don't blame ya), then start hydrating her now.
It could also be the beginning symptoms of a heart attack or stroke. What you need to watch for with a heart attack, is pressure building on her chest. It will start to feel like a horse is sitting on her chest, and like she can't breath. Also, most arm pain that is associated with heart attacks, is in the left arm. With a stroke, you'll want to watch for confusion, slurring her words or droopy facial features. If you sense any of these things, it's time to call the ambulance or get to the nearest hospital ASAP.
The truth though, is that most people who think they are having a heart attack or stroke, aren't. Try getting her to drink A LOT of water, and peeing a lot. If her pee is anything other than clear (like water), then she is dehydrated. Also, depending on her age, it could be part of menopause.
These are just some ideas. I hope she feels better!